JP4582517B2 - X-ray tube cathode filament manufacturing method and X-ray tube - Google Patents

Description

  In one embodiment, the present invention relates to a method for producing an X-ray tube cathode filament. More particularly, the present invention relates in one embodiment to a method that can be used to obtain a unitary cathode filament. The invention also relates in one embodiment to an X-ray tube comprising such a cathode filament.

  The present invention can be applied, in one embodiment, to x-ray tubes, particularly mammography (mammography), x-ray tubes used in devices or scanners used to study the vascular system. In medicine, a device commonly used as a cathode that emits an electron beam (cathode) is a cathode filament. At least one anode is arranged facing the cathode filament. Electrons emitted by the cathode filament collide with the anode at high speed. At that time, the anode emits X-rays.

  For use in medicine, it is necessary to increase the accuracy of positioning of the cathode with respect to the anode in order to generate X-rays. If the position of one of these elements changes by more than 10 micrometers relative to its intended position, it can adversely affect the precise control of x-ray generation. During X-ray generation, the cathode filament reaches a temperature of about 2800 ° C. Accordingly, the cathode filament expands. The expansion of the cathode filament may cause the cathode filament to move relative to the anode. This expansion can also cause damage to the filament.

  Some known cathode filaments have three parts. That is, it has a filament body supported by two legs. The filament body emits electrons. The two legs of the filament are parallel to each other and perpendicular to the filament body. These legs are soldered to the two ends of the main body, respectively. The soldering method not only requires delicate manipulation, but also makes the cathode filaments brittle at the location of these solder areas. Thus, the filament can break at the location of these solder areas during expansion.

  In order to solve the problem of mechanical weakness between the filament body and the legs, the known method uses a single cathode filament. The filament is manufactured from a single plate that is curved in a U-shape. Thus, the two legs of the body forming the filament are made in one piece. Therefore, the soldering process is eliminated.

The single filament obtained is mechanically robust. However, the thickness of the leg is the same as the thickness of the main body. Therefore, the rigidity of the obtained filament is large. During the use of an X-ray tube with this type of cathode filament, the cathode filament body has a greater degree of expansion than the legs. The mechanical resistance of the main body is reduced, which causes the main body to move. The length of the filament body increases with this expansion. Since the expansion of the leg is relatively small, the leg is stiff and prevents the filament body from stretching. Therefore, the filament body undergoes plastic deformation to the extent that it is curved. Accordingly, the position of the cathode relative to the anode is changed relative to the initial position. Once deformed, the filament body emits electrons in all directions. In medical engineering, it is often desirable that the electron emission surface should be maintained at a right angle to the anode facing it. If the body deforms uncontrollably, the filament can no longer be used.
US Pat. No. 5,283,085

  Thus, conventional cathode filaments are not satisfactory. Filaments with the body soldered to the two legs can break at the location of the solder area when the filaments expand. In addition, a single filament may be deformed when it expands, changing the anode-cathode distance. This is contrary to the efficient operation of the X-ray tube enclosing the filament.

  In one embodiment, the present invention, in order to solve the above-described problem, produces a single cathode filament that can have a leg thickness different from a body thickness according to the disclosed method. Since the filament obtained in one embodiment of the present invention is a single filament, the possibility of leg breakage relative to the filament body is generally avoided. Further, since the thickness of the legs and the thickness of the body are independent, these thicknesses can be varied to create a flexible leg for the body. Thus, when the filament expands, the legs can spread out so as to be spaced outward. Therefore, it is possible to cause the extension of the filament body in the planar direction so as not to change the distance between the cathodes facing each other and the anode. The cathode filament to be manufactured is a filament whose legs are sufficiently flexible to absorb deformation of the filament body due to expansion.

  One embodiment of the present invention is directed to a method of manufacturing a cathode filament for an x-ray tube that has at least two legs and a body and is a single filament. One embodiment of the method comprises the steps of spraying at least one material onto a support, for example by plasma spraying or other deposition techniques, to obtain a filament molded on the support. Separating the filaments formed from the support. One embodiment of the present invention is also directed to an x-ray tube with at least one cathode filament provided by one embodiment of the method.

  One embodiment of the present invention will be more clearly understood from the following description and the accompanying drawings. The drawings are for display purposes only and do not in any way limit the scope of the invention.

  In one embodiment of the invention, it is proposed to make the cathode filament by plasma spraying. Plasma spraying is a thermal spraying process. The solid product is melted or softened by a heat source and sprayed in the form of fine particles on a previously prepared surface. For this purpose, the combustion energy from the plasma jet is used. A plasma is an ionized medium, ie, a medium composed of a mixture of ions and electrons and neutral species that can or cannot be excited. A torch with two electrodes is used to perform the plasma spray. The torch takes the form of a conical cathode within a cylindrical anode that forms a nozzle. An inert gas such as argon is flowed between the two electrodes where the gas is ionized to form a plasma. A tube is used to introduce the material to be sprayed into the plasma jet in the form of a powder. The material itself to be sprayed is conveyed by neutral gas. The ejected particles reach the substrate in a highly melted state at a high speed in the range of a few hundred meters per second. The particles rush into the substrate and cool rapidly, stacking together, thus gradually forming a deposit.

  In one embodiment of the invention, plasma spraying is used to produce filaments from the desired material.

  FIG. 1 shows a filament 1 made on a support 2 by plasma spraying. The production method starts with the production of the support 2. The outer contour of the support 2 is made to correspond to the contour to be obtained for the filament 1. Depending on the mechanical properties to be applied to the cathode filament 1, one or more types of materials to be sprayed in powder form on the support are selected. For example, tungsten powder is sprayed. In this way, the cathode filament 1 made of tungsten is obtained at the end of the plasma spraying operation.

  In another exemplary embodiment, the sprayed plasma can be an alloy of tungsten powder and rhenium powder. Specifically, the resulting tungsten / rhenium mixture imparts anti-aging properties to the cathode filament 1. Tungsten is known to form giant crystals over time. These giant crystals weaken the structure of the filament 1 or reduce the rigidity of the filament 1. On the other hand, rhenium is known to limit the spread of giant crystals throughout the structure forming the filament 1. Thus, the production of this type of rhenium-tungsten filament extends the life of the cathode filament 1.

  In another exemplary embodiment, several successive plasma sprays can be performed using different materials each time. Accordingly, the obtained cathode filament 1 is a single unit, but a unit having a mixed composition. In other words, the cathode filament is formed by several successive layers of different materials. The materials used can be selected as a function of their mechanical or chemical properties, depending on user requirements.

  In one embodiment of the method for producing the cathode filament 1 by plasma spraying, the cathode filament 1 having the required thickness is obtained. The thickness of the filament 1 changes according to the time for which the plasma spray is applied to the support. Also, the time of plasma spray 5 applied to the portion 6 in the support 2 for molding the body 8 of the filament 1 is applied to the portion 7 in the support 2 for molding the leg 9 of the filament 1. The time for applying the plasma spraying operations 3 and 4 can be longer.

  Therefore, as shown in FIG. 2, it is possible to make a filament 1 in which the thickness D of the main body 8 is larger than the thickness d of the legs 8. Thereby, the leg part 9 is more easily bent than the main body 8. This flexibility of the legs 9 relative to the body 8 of the filament 1 allows the body 8 to stretch linearly and in a planar direction, and each leg 9 is twisted outwardly relative to the body 8 of the filament 1. It is. For example, the thickness D of the main body 8 is 100 to 300 microns, and the leg thickness d is 50 to 150 microns. In a specific example, the thickness d of the two legs 9 is the same. In one specific exemplary embodiment of the present invention, the cathode filament 1 is made such that the thickness D of the body 8 is about 200 microns and the thickness of its legs 9 is about 100 microns.

  In one embodiment of the manufacturing method of the present invention, the method includes a step of spraying one or a plurality of types of materials on the support 2 manufactured in advance by plasma spraying 3, 4 and 5. The filament 1 thus obtained is taken out by separating the filament 1 from the support 2. The support 2 can be made from one or more types of materials that can then be selectively dissolved in a chemical solution. The term “selectively dissolved” is understood to mean that only the support 2 is dissolved and that the filament 1 is insoluble in the chemical solution. In the next step, tungsten powder is sprayed onto the support 2. After a desired cathode filament 1 having one or more desired thicknesses d and D is obtained in this way, it is formed by a filament 1 made of tungsten and a support 2 made of titanium, zirconium and molybdenum. Immerse the unit in a special solution. In this solution, the support 2 is dissolved, but the filament 1 is not dissolved.

  In another exemplary embodiment of the invention, the support 2 can be made of graphite. Graphite cannot be selectively dissolved by chemical solutions. However, it can be planned to coat the support 2 made of graphite with an intermediate layer which is selectively and chemically soluble. For example, a rhenium intermediate layer is sprayed onto the graphite support 2 by plasma spraying. For example, rhenium is selectively dissolved in a solution containing nitric acid. After covering the support 2 with the intermediate layer made of rhenium in this way, plasma spraying 3, 4 and 5 is carried out with the material (one type or plural types) selected for forming the cathode filament 1. The unit formed by the support 2 and the filament 1 is then placed in a nitric acid-containing solution at 40-50 ° C. within a range of 1-15 minutes, depending on the thickness of the rhenium intermediate layer to be dissolved. Soak for a period of time. Once the rhenium intermediate layer is dissolved, the cathode filament 1 and the graphite support 2 are taken out separately.

  In one embodiment of the method of the invention, it is possible to produce cathode filaments 1 of any shape. Depending on the outer contour of the support 2, the filament 1 has a different contour.

  It is also possible to make the main body 8 of the cathode filament 1 having a winding shape as shown in FIG. The machining is performed, for example, by “electric corrosion (electric discharge machining)”. The term “electric corrosion” is understood to mean wire cutting. In order to form an electric arc between the wire and the part to be cut, the wire is driven to rotate at high speed. When the wire is brought close to the part to be cut, the material is released very accurately. Thus, a notch 10 can be made having a width of 40-80 microns, preferably 50-60 microns, and a depth of 0.5-3 mm, preferably 1.5 mm. Depending on the user's requirements and the initial length of the body 8 of the filament 1, various numbers of notches 10 can be made. In one particular embodiment of the invention, ten notches are made and distributed in an array of five on each side 11 and 12 of the body 8 of the filament 1.

  In an exemplary embodiment of the method, the filament 1 is machined while the filament 1 is still on the support 2. After making the notch 10 in the filament 1 and the support body 2 by machining, this support body 2 is melt | dissolved and the winding filament 1 is taken out.

  In another exemplary embodiment of the method, the filament 1 can be separated from the support 2 before making the notch 10 by machining. The mechanical resistance of the filament 1 obtained by one embodiment of the method of the present invention can be large enough to allow machining of the filament 1 separated from the support 2.

  One embodiment of a method of manufacturing the cathode filament 1 can be used to obtain a single filament 1 having a desired variable thickness d and D. The thicknesses d and D may be different values at the positions of the main body 8 and the leg 9, and the thicknesses d of both legs 9 may also be different from each other.

  It is also possible to change the mechanical properties of the filament 1 by choosing an appropriate material for performing the plasma spraying. It is also possible to combine the chemical and mechanical properties of different materials to form a filament 1 made from a specific alloy to meet precise requirements. Complex shaped filaments 1 can be easily made without the need for any soldering process that could weaken the filaments 1.

  The filament 1 obtained by one embodiment of the present invention can positively position the cathode with respect to the anode (not shown). The expansion that occurs in the body 8 of the filament 1 does not change the position of the body 8 relative to the anode. As a result of the flexibility of the legs 9 with respect to the body 8 of the filament 1, the body 8 stretches linearly and in a planar direction, and the legs 9 are each twisted outwardly with respect to the body 8 of the filament 1.

  An embodiment of the invention also relates to an X-ray tube with a cathode filament 1 made according to various examples of the method described above.

  Those skilled in the art will be able to make various changes to the functions and / or methods and / or results and / or structures and / or steps of the disclosed embodiments and their equivalents without departing from the scope of the invention. I can do it.

It is a schematic diagram which shows the example of operation which plasma-sprays material on a support body in order to form a filament. It is a perspective view which shows the obtained cathode filament.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Filament 2 Support body 3, 4, 5 Plasma spraying operation 6 Support body part for molding the filament main body 7 Support body part for molding the filament leg part 8 Filament body 9 Filament leg part 10 Notches 11, 12 Side

Claims (15)

A method for producing a cathode filament of an X-ray tube, comprising:
The method includes the steps of forming a filament that has at least two legs and a body and is a single body filament, the step comprising:
Spraying at least one material onto the support by plasma spray to obtain a filament molded on the support;
Separating the obtained filament from the support;
A method characterized by comprising. The method of claim 1, wherein the material sprayed by plasma spray to form a filament is tungsten. The method according to claim 1 or 2, wherein the material sprayed by plasma spraying to form a filament is an alloy of tungsten and rhenium. 4. A method according to any one of claims 1 to 3 comprising the step of spraying different materials onto the support in succession by plasma spraying to form filaments of the mixed composition. 5. The method according to claim 1, further comprising the step of plasma spraying to obtain a filament having a filament leg thickness (d) that is different from the filament body thickness (D). The method according to item. 6. The method of claim 5, wherein the thickness of the body is from 100 microns to 300 microns and the thickness of the legs is from 50 microns to 150 microns. Making the support from a material that is selectively and chemically soluble;
Dissolving the support after making the filament by plasma spraying;
The method according to claim 1, comprising: The method of claim 7, wherein the support is formed of an alloy of titanium, zirconium and molybdenum. Making the support from a material that is not chemically soluble;
Coating the support by plasma spraying with an intermediate layer formed of a material that is selectively and chemically soluble;
Melting the intermediate layer after making the filament by plasma spraying;
The method according to claim 1, comprising: 10. A method according to claim 9, wherein the insoluble support is made of graphite and the material forming the intermediate layer is rhenium. 11. A method according to any one of the preceding claims, comprising machining the body of the filament to obtain a body having a winding shape. Machining the filament body on the support;
Separating the machined filament from the support;
12. The method of claim 11 comprising: Separating the filament from the support;
Machining the body of the filament;
12. The method of claim 11 comprising: 14. A method according to any one of claims 11 to 13, wherein the filament body is machined by electrolytic corrosion. The X-ray tube provided with the cathode filament obtained by the method of any one of Claims 1-14.

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